1. Field of the Invention
The present invention relates to an adsorption member for ink jet use and an adsorbent used for the adsorption member, as well as to an ink retaining container provided with such member. The invention also relates to an ink supply system and an ink jet recording apparatus, which use such ink retaining container.
2. Related Background Art
In the field of the ink jet technologies, it has been known that liquid droplets are discharged by use of an ink jet head, which is arranged to activate the discharge elements, such as the heat generating elements that produce foaming phenomenon or the eletromechanical converting members that convert electric energy into the solid displacement in the ink (liquid) supply route.
For an ink jet of the kind, there is used exchangeably or integrally the liquid paths that performs ink supply continuously, the liquid chamber that perform the liquid supply efficiently, the supply tubes for use of ink supply to these liquid flow paths and liquid chamber, and the ink tank (ink retaining container) for use of ink supply to the supply tubes and the like.
Then, it is often practiced to provide the ink supply route, particularly the ink retaining container, with the foaming member or the aggregate fibrous member capable of absorbing or holding ink, which is formed from the polymeric resin (including rubber), for generating negative pressure and/or preventing the liquid level from being fluctuated due to the vibration of the carriage. Of course, the ink retaining container and the ink flow route themselves are often molded with polymeric resin.
Now, however, when using the polyurethane foam which is known as an inexpensive foaming member whose foaming is easily controllable, there are some cases where the unreacted substance created in the foaming process or the polyurethane bond which has a weaker bonding force is eluted into ink. If an ink retaining container having such eluted substances in it is used, there is encountered a problem which has been objectively recognized as to exert influence on the ink supply itself at the earlier stage thereof. The typical patents to deal with this condition are such as disclosed in the specifications of Japanese Patent Laid-Open Application Nos. 64-26452 and 04-348947, wherein before the absorbent itself is provided in the ink retaining container, cleaning is conducted in advance so as to remove the eluted substances retained in the ink jet head at the early stage of ink supply. The technique thus invented is effective in that the ink supply capability is brought to the practical level from the very beginning of ink supply to the head.
Also, in the specification of Japanese Patent Laid-Open Application No. 62-60653, it is recognized as a problem that the insoluble substance of the ink retaining container itself is eluted into ink to exert influence on its ink supply performance.
In other words, it is known that the structure, which is needed to supply ink to the ink jet head (ink retaining container main body) itself, is fabricated in the process of manufacture so as not to allow the insoluble substance inherently gained by such structure to exert any influence on ink discharges when this structural member is used for ink supply to the ink jet head.
Nevertheless, in accordance with the researches and studies of the inventors hereof, when the ink retaining container having the absorbent which has been cleaned as described above is exchanged for use repeatedly for a number of times, there are some cases where the ink discharge itself is affected. Then, depending on the cases, it is observed that the images formed by discharged ink droplets themselves present some ink spread or excessive permeability of ink (the phenomenon where ink is permeated thoroughly from the surface to the back side of a recording sheet).
The inventions hereof have assiduously studied to analyze and clarify the causes of the creation of these phenomena. As a result, it has been found that the members which have been formed with the polymeric material, such as the ink retaining container, the absorbent, used for the formation of the ink supply route, are caused to elute the material continuously in such a minute quantity of less than ppm unit that cannot be measured along with the temporal passage. Then, the eluted substance is accumulated gradually in the portion (ink flow paths, for example) which is related to the ink discharges of the head (conceivably, such substance is collectively increased and retained in one specific portion or another), and then, the accumulated substance begins to exert influences on discharges. Further, due to some action, the insoluble substance thus accumulated is allowed to be contained in ink droplets, and discharged together with them.
Particularly, in recent years, the printer that prints the photographic images should perform the highly precise impact of smaller droplets, and the ink discharge performance of such printer is easily affected by the presence of substance slightly eluted from the ink retaining container or by the presence of hydrophobic substance such as the intermediate product of dyestuffs.
Further, there is a tendency in recent years that the droplets of discharged ink themselves are made smaller still in order to perform highly densified recording. Along with this tendency, the discharge openings (ports) are made smaller. Also, the discharge pressure generating unit, such as the electrothermal converting members, is arranged in higher density. As a result, the sectional area of each of the ink supply paths becomes smaller. Likewise, the recording speed is also made faster. To meet such requirement, the discharge speed of liquid ink becomes increasingly faster.
It has also been found that this tendency is easier to take place particularly in condition that the amount of discharge ink droplet is smaller (15 pl or less, for example) or the head is arranged in a higher density (such as the discharge openings (ports) or the flow paths are allowed to deal with 600 dpi or more), and that the pH of ink used is higher, and the recessed portions, stepped portions, or curbed passages are present in the ink supply route. This tendency is also found in a case where either one of the discharge speeds, response frequency, and discharge energy is made higher, or in a case of a head that utilizes the creation of bubbles, while allowing the air outside and bubbles to be communicated with each other.
Further, it has been found that the above phenomenon appears more often when discharges are made after a comparatively long rest subsequent to the discharges having been made once from an ink jet head, and that it appears in the initial stage of discharges after a long rest.
The present invention is designed on the basis of such knowledge that has never been recognized in the conventional art. The invention will be described more specifically as follows:
For example, in the urethan foam which has been produced, there is initially a considerable residue of unreacted substance of such materials as polyol, interfacial active agent, foaming agent, higher alcohol, catalyzer, or the like.
Further, in a case of the foam processed in a specific shape after the thermal press that has been given for a long time at higher temperature, bonding is cut off in this process, and then, free polyol or the like is present in a considerable amount initially. When ink is filled in the absorbent formed by such polyurethane foam, the unreacted substances and the thermally decomposed substance described above are gradually eluted into ink and aggregated, hence being accumulated or lowering the surface tension and pH of ink. As a result, the print quality of characters and images is degraded.
Also, when the container and absorbent are formed by polyolefine fabric, the fabric and the formed product contain the derivative of higher fatty acid, such as calcium stearate, serving as the neutralizer or lubricant. These are eluted into ink (particularly the elution is conspicuous when the absorbent is produced by the application of thermal formation). Here, it has been observed that an elution of the kind does not present any problem in the ink flow paths, but it tends to disturb the ink discharge characteristics when eluted substance adheres to the circumference of the discharge openings (ports).
Hereunder, the examples of phenomena will be simply enumerated as observed in recording performed by use of a head of the kind as follows:
For example, with the discharge amount of 15 pl, there is not greater influence on the twisted prints, but spreading of ink takes place, resulting in the blurred print quality in some cases. With the discharge amount of 10 pl or less, for example, the greatly twisted prints are observed in some case. At 8 pl, for example, the discharge directions are caused to fluctuate in particular. Also, in the 600 dpi, the discharge amount is more or less 20 pl, but in 1,200 dpi, it becomes 8.5 pl to bring about the conspicuous twisting. For the minute ink droplets, it is preferable to suppress the twisting itself to approximately a half of the allowable twist of the ink discharges in 600 dpi, for example. However, in some cases, it is still observed that the twisted condition is beyond this range.
Particularly, when the discharge amount is set at 8.5 pl, it is observed that discharge is directed completely different after the head is left intact for several minutes. This tendency is proportional to the amount of resultant elution of polyol to ink, and the print quality is degraded accordingly.
Here, also, in order to stabilize the discharges, the application of energy (voltage and pulse width) should be increased. Then, the twisted ink droplets become more noticeable eventually.
Further, the temperature of heater substrate rises as the number of printing sheets becomes more. Then, twisting is increased.
Also, the method for sucking ink or wiping off the eluted substance periodically together with ink makes it possible to reduce the eluted substance in the flow paths, but it is still difficult to remove the eluted substance which has adhered to the orifice surface. As a result, it is difficult to improve all the twisting conditions that may be caused by the deviated direction of discharges.
Moreover, even with the execution of the sucking operation, there are some cases where twisting becomes noticeable after having printed on only one A3-sized sheet. Therefore, suction should be executed more often, which necessitates the provision of the increased capacity of a waste ink retaining container after all. Also, in order to enhance the printing speed, the discharge frequency should be increased to 20 kHz as currently required from the conventional frequencies of 8 to 10 kHz, for example. Then, the temperature of the heater substrate is caused to rise earlier and increase the twisting still more.
Also, while a tendency of the kind being confronted, it has been demanded to reduce the replacement frequency of ink retaining containers. As a result, the size of the ink retaining container has become larger inevitably, and the ink absorbent installed in it has also become larger accordingly. The amount of eluted substance tends to be increased under the circumstances.